1. Field of the Invention
This invention relates to bearings and is particularly, but not exclusively, applicable to bearings for railway vehicles. Certain types of railway bearings are described in our British Pat. No. 1464177 wherein a cylindrical bearing liner is mounted in a bearing housing and has a cylindrical bearing surface to receive the axle from one end of the housing. The housing includes a hollow end cap secured to the other end to provide a reservoir for holding a lubricant supply and a delivery passage for lubricant extends from the reservoir to a bottom region of the bearing surface of the bearing liner to permit flow of lubricant from the reservoir to the liner. The housing also provides oppositely facing annular thrust faces for engaging oppositely facing thrust faces on the axle.
Lubricant, usually grease, is inserted into the housing through a filler plug and is generally intended to last for the life of the bearing which is sealed at its inboard end by means of a lip seal mounted in the housing between the housing and the axle. It has been found in practice that under certain conditions of volume of grease within the housing and end cap and at certain high temperatures, excessive pressure is developed inside the housing which may adversely affect the operation of the seal. Also in certain constructions of bearings of the type described in British Pat. No. 1464177, noteably those wherein the axial thrust faces are provided on opposite sides of an end disc secured to the axle, the effect of the axles rotation coupled with the axial oscillation of the disc occurring in use tends either to exert excessive pressure on the inside of the seal at the inboard end of the housing or to discharge lubricant through any simple form of breather which has not been designed to separate air from lubricant. It will be appreciated that some form of breather is required in the end cap to relieve the air expansion which occurs as the running temperature rises.
It is an object of the present invention to provide a new or improved construction of bearing which will obviate the problems referred to above.